AB0846 EFFICACY OF RITUXIMAB IN IDIOPATHIC INFLAMMATORY MYOPATHIES. EXPERIENCE ON 36 PATIENTS FROM A PROSPECTIVE MONOCENTRIC COHORT
Authors: A. Gamba, L. Iaccarino, E. Cocconcelli, E. Zanatta, R. Depascale, L. Ienna, E. Balestro, M. Zen, M. Gatto, A. Doria
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Idiopathic inflammatory myopathies are a heterogeneous group of autoimmune disorders characterized by muscle inflammation frequently associated with the involvement of other organ systems. Due to variety of presentations and severity degree, treatment of inflammatory myopathies is challenging. Considering the immunopathogenic role of B cell in myositis, Rituximab (RTX), as B cell depleting agent, could be an effective therapy in patients refractory to others immunomodulatory drugs. <h3>Objectives</h3> The aim of the present study is to demonstrate the efficacy of RTX for the treatment of idiopathic inflammatory myopathies in multi refractory patients. We also considered the effectiveness of a low-dose RTX as a remission-maintenance therapy. <h3>Methods</h3> From a monocentric cohort of patients with inflammatory myopathies, we considered all patients who have been treated with RTX (2 infusions of 1 gram, week 0-2). We also considered low-dose RTX as a single dose of 1g every 6 months. The response to RTX was considered based on physician judgement (complete CR, partial PR, no-response NR), focused on muscle and lung manifestations. Improvement in muscle involvement was based on reduction of 30% of creatine kinase levels and/or an increase in Manual Muscle Test score (MMT-8) of 20%. Interstitial Lung disease (ILD) was evaluated by pneumologist judgement based on chest computer tomography and spirometry. A response was considered partial if it was maintained less than 6 months from RTX administration and complete if it persisted more than 6 months. <h3>Results</h3> Thirty-six patients were included, 15 with diagnosis of polymyositis, 13 with antisynthetase syndrome, 6 with dermatomyositis, 1 with inclusion body myositis and 1 with necrotizing myopathy. Anti-Jo1 autoantibodies were found in 12 patients, anti-SSA in 9, anti-SRP in 5, anti-PM/Scl 75 in 2, anti-Mi2 in 2, anti-PL7 in 1, anti-PL 12 in 1, anti-SSB in 1, anti-TIF1-γ in 1, anti Ku in 1 and anti Sp100 in 1. Most patients (50 %, n=18) were treated with RTX for muscle involvement, 17 % (n= 6) for ILD, 33 % (n=12) for both muscular and lung disease. All patients received oral glucocorticoid before starting RTX administration. The others previous therapies were: methotrexate in 72% of patients, mycophenolate mofetil in 50%, IVIG in 27%, azathioprine in 22%, hydroxychloroquine in 14%, cyclosporine in 14%, leflunomide in 11%, tacrolimus in 3%, cyclophosphamide in 3%. We observed CR to RTX in 70% of patients, PR in 19%, NR in 11%. In the subgroup treated for muscle involvement (n=18), we found a CR in 10 patients, a PR in 5 and NR in 3. In patients with ILD, 5 patients got a CR and 1 PR. In the group of patients with both lung and muscle manifestations, we observed 10 CR, 1 with PR and 1 with NR. Five patients were treated with a low dose maintenance therapy after having achieved remission with standard dose. Three patients had a diagnosis of polymyositis, one of dermatomyositis and one of antisynthetase syndrome. Patients received a minimum of 3 infusions and a maximum of 5 infusions of low dose RTX.Therapy was administrated for an average of 3 years. All of them maintained a CR to RTX. <h3>Conclusion</h3> In our cohort, RTX was effective in 89% multi-drug refractory patients and the low-dose was efficacious as a maintenance therapy in all cases. <h3>References</h3> [1]Oddis CV et. al. Rituximab in the treatment of refractory adult and juvenile dermatomyositis and adult polymyositis: a randomized, placebo-phase trial. Arthritis Rheum. 2013 Feb;65(2):314-24. doi: 10.1002/art.37754. PMID: 23124935; PMCID: PMC3558563. [2]Schmidt J. Current Classification and Management of Inflammatory Myopathies. J Neuromuscul Dis. 2018;5(2):109-129. doi: 10.3233/JND-180308. PMID: 29865091; PMCID: PMC6004913 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.